Communication devices such as User Equipments (UE) are also known as e.g. Mobile Stations (MS), mobile terminals, and wireless terminals. UEs are enabled to communicate wirelessly in a wireless communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two UEs, between a mobile station and a regular telephone and/or between a mobile station and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications network.
Examples of wireless communication systems are Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS) and Global System for Mobile communications (GSM).
UEs may further be referred to as mobile telephones, cellular telephones, laptops, or tablets with wireless capability, just to mention some further examples. The UEs in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another mobile station or a server.
The wireless communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a Base Station (BS), e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the UEs within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
Communication in Radio Networks
When communicating over a wireless link a wireless node needs information about the procedure for receiving data, and in the case of a scheduled Medium Access Control (MAC) protocol also how and when to transmit data. The procedure for receiving data may be governed by transmission parameters.
Most radio access technologies use scheduled radio access wherein two wireless nodes, such as a base station and a wireless communications device, may send payload data after first negotiating about transmission parameters. Generally, the radio access schemes using scheduled radio access aim to be resource efficient for receivers and to avoid collisions on radio resources.
LTE will be used here as an example. When a UE wants to have access to uplink spectrum in LTE in order to send for example payload data in uplink there is a periodic resource for scheduling requests from the UE.
A scheduling request from the UE is followed by an uplink grant sent from the base station to the UE. The uplink grant enables the UE to transmit the payload data in uplink.
FIG. 1 illustrates parts of a prior art wireless communications network, exemplified as an LTE network. In the prior art wireless communications network a first base station BS1 may communicate directly with one or more UEs as described above. For example, the first base station BS1 may communicate directly with a first user equipment UE1 or a second user equipment UE2. However, in some circumstances it may be beneficial for the first base station BS1 not to transmit data directly to the first user equipment UE1 or the second user equipment UE2, e.g., sometimes the first user equipment UE1 cannot be reached directly for some reason, due to e.g. the physical location of the first user equipment UE1. The first base station BS1 may as an alternative transmit the data intended for reception by the first user equipment UE1 to a second base station BS2, which may relay or forward the data to the first user equipment UE1. A similar relaying method is possible for transmitting data to the second user equipment UE2 via the second base station BS2, or via the first user equipment UE1. The above examples were given for DL communication. However, without going into details similar examples may be given for the UL. Networks making use of such relaying or forwarding as described above may be referred to as multi-hop networks.
Multi-Hop Networks
A multi-hop network is a wireless communications network adopting multi-hop wireless technology without deployment of wired backhaul links. Categories that may be used are for example: relay and mesh. The relay category may have a tree based topology, wherein one end of the path may be a base station.
The mesh category has a mesh topology, wherein multiple connections are possible among user equipments. Benefits of multi-hop technology may be:
Rapid deployment of the multi-hop network with lower-cost backhaul;
Easy to provide coverage in areas that are hard to wire;
Extended coverage due to multi-hop forwarding;
Enhanced throughput due to shorter hops; and
Extended battery life due to lower power transmission.
Relaying in multi-hop networks may for example be used when a UE cannot be reached directly and/or for inband self-backhauling. In inband self-backhauling a base station uses the same frequency band for the backhaul and for the radio access. This may for example be used when a base station does not have access to wired backhauling. In a hierarchical telecommunications network the backhaul portion of the network comprises the intermediate links between the core network and the small subnetworks at the “edge” of the entire hierarchical network. The small subnetworks at the “edge” is in the context of wireless communications networks the radio access network. Sometimes it may be cheaper both in terms of radio resource consumption and in cost to use inband self-backhauling. Inband self-backhauling has been identified to simplify deployments for 5th generation (5G) mobile networks.
Although scheduled radio access communication works well for a single link, there are several drawbacks when scheduled radio access communication is used in multi-hop relay networks. For example, it takes a lot of time and overhead resources to set up the links between the nodes in each link in a multi-hop relay chain.
In some scenarios prior art techniques does not work, for example, if the nodes in the multi-hop relay chain are unknown or if the protocols stacks in the nodes are not yet initiated.